The pathogenesis of extensive discovertebral destruction in ankylosing spondylitis.

The study of extensive discovertebral destructive lesions in ankylosing spondylitis has been largely limited to isolated case reports or clinicoroentgenologic reviews with little pathologic correlation. In eight specimens of the spine collected from 35 patients with ankylosing spondylitis showing extensive discovetebral destructive lesions, a detailed pathologic study revealed a consistent picture of complete or near-complete destruction of the disc-bone border and the intervertebral disc. The disc was replaced by fibrous tissue and/or fibrocartilage showing moderate to severe fibrinoid necrosis and cystic degeneration. Such changes are characteristic of pseudarthrosis, which may follow either fracture or degeneration of the disc perpetuated by abnormal stress and motion. The reparative process included fibrovascular tissue proliferation from the vertebral bone marrow. Fibrovascular tissue also perforated the vertebral end-plate and intervertebral spaces resulting in massive discovertebral destruction. Pathologic observations strongly implicate mechanical trauma and pseudarthrosis as initiating and perpetuating extensive discovertebral destruction in ankylosing spondylitis.